Production of foamed polyolefins in a high shear zone



H. N. COYNER 3,108,148 PRODUCTION OF FOAMED POLYOLEFINS IN A HIGH SHEAR ZONE Oct. 22, 1963 Filed June 19. 1959 POLYMER INVENTOR. H.N. COYNER BY Z4 5 A T TORNEYS United States Patent "ice 3,108,148 PRODUCTION OF FOAMED POLYOLEFINS IN A HIGH SHEAR ZONE Herbert N. Coyner, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed June 19, 1959, Ser. No. 821,552 1 Claim. (Cl. 261-141) This invention relates to foamed polymers of aliphatic l-olefins. In one aspect, this invention relates to foaming of polyolefins with a gas in a high shear zone. In another aspect, this invention relates to an apparatus particularly adapted for foaming polymers of l-olefins.

It is an object of this invention to provide a novel apparatus particularly adapted to foaming polymers.

Other objects, features and advantages of this invention will be obvious to those skilled in the art from the following detailed description and discussion.

The apparatus of this invention comprises in combination an elongated cylindrical tubular member having smooth internal surface and being perforated at one end, means for introducing polymer at the opposite end, means for introducing gas to said tubular means remote from the perforated end, means for imparting a longitudinal shearing action in said tubular member and means for maintaining a temperature gradient along said tube, the highest temperature being at the end having means for introducing polymer.

The length of the dispersion zone will ordinarily be from 10 to about 50 times the inside diameter although greater or lesser lengths can be employed. Concentrically located in this zone is a smooth rod which rotates at a speed in the range between 10 and 1500 r.p.m., preferably between 100 and 1000 r.p.m. The diameter of the rotating rod will be from about 0.25 to 4.0 inches or more. The radial distance from the surface of the rod to the wall of the dispersion zone will generally be in the range between 0.5 and 4.0 inches, preferably not more than 2 inches, the larger dimension being used when operating with a rotating rod of larger diameter. In any case, the diameter of the zone in which the concentrically disposed rod is rotated is such that a shear is created in the resin between the rod and the walls thereof.

The rotating rod can be made of any metal or material with which there is at least some adhesion to the molten mass. Suitable materials include steel, stainless steel, aluminum alloys, brass, bronze, high melting point plastics, hard woods, etc. It is desired that the rod be smooth and circular in cross-section and that the tubular member in which it rotates also be smooth and of circular cross-section since the presence of baflies, impellers and the like create areas of variation in shear, resulting in nonhomogeneous admixture of the gas. This rotating rod generally will extend from three-fourths to the entire length of the tubular member, however, to obtain a full volume of foam, it is preferred that the rod extend threefourths to nine-tenths the length of the tubular member.

At the exit end of the tubular zone is disposed a grating of such nature that a pressure gradient is created between its upstream and downstream faces. The molten resin, at this point only a few degrees above its congealing temperature, e.g., 5 to 25 F., passes through this barrier, from a region of higher pressure to one of lower pressure, thereby permitting expansion of the occluded gas.

3,108,148 Patented Oct. 22, 1963 From this point, the resin passes out through a nozzle into a mold, a sheeting device, or other suitable recovery means.

This invention will be further described in conjunction with the drawing which is a cross-section of a preferred embodiment of the apparatus of this invention.

Referring to the FIGURE, molten polymer is introduced to zone 1 via conduit 2 under suitable pressure, e.g., 5 p.s.i.g. or higher, and a gas such as air is injected through conduit 3 at approximately the same pressure as that of the molten resin. Dispersion rod 4, concentrically located in zone 1 of tubular member 1a, is rotated by a belt, not shown, on pulley 5 or by some other suitable power means. This rod 4 is supported by bearings 13 and 14, bearing 13 being supported by a suitable spider. Temperature in the dispersion zone is regulated by heating coils 6, 6a and 612 so disposed that temperature can be maintained at a level sufficiently high that the resin is in a flowable state but progressively reduced in temperature as it moves along tube 1a. At the downstream end of dispersion zone 1, the gas containing melt encounters barrier 7 containing perforations 7a. The pressure drop across the barrier from zone 1 to zone 8 causes the polymer to expand in cellular form. The temperature in zone 8 and the nozzle section is maintained sufficiently high by means of heater 12 that the foamed mass continues to flow and is discharged through nozzle 9 to belt 10. This moving belt 10 is used to carry the foamed polymer under blade 11 which is adjustably mounted to sheet the polymer out to the desired thickness.

Those skilled in the art will see many modifications which can be made and still obtain the advantages of this invention. For example, alternatively from the design shown in the drawing, the blowing gas can be admitted at several points around the periphery of the dispersion zone and along the dispersion zone. These points of addition will be in the upstream portion of said zone. Another alternative is to introduce the gas through dispersing rod 4, said rod being hollow with orifices provided near the upstream end.

I claim:

An apparatus particularly adapted for foaming synthetic resins,

said apparatus comprising, in combination:

an elongated cylindrical tubular member having a smooth internal surface;

means for closing one end of said tubular member;

a concentrically and axially disposed smooth cylindrical rotatable member mounted in said tubular member; means for rotating said rotatable member;

inlet means near said one end for introducing resin into said tubular member;

inlet means near said one end for introducing gas into said tubular member; heating means for maintaining a temperature gradient along said tubular member with the highest temperature being at the end remote from said other end;

an enlarged housing provided with a discharge nozzle and heating means connected to said other end of said tubular member;

and a perforated barrier at the exit end of said tubular member through which resin and gas pass disposed between said housing and said tubular member, said barrier being adapted to create a pressure gradient between the upstream and downstream faces of said barrier so as to cause foaming of resin by expansion of occluded gas.

References Cited in the file of this patent UNITED STATES PATENTS McIntire July 18, 1950 Veit Jan. 8, 1952 Duddy Apr. 27, 1954 Toulmin Sept. 21, 1954 Willert Mar. 19, 1957 Von Kohorn Mar. 25, 1958 Gray Mar. 15, 1960 Rubens et a1. Dec. 4, 1962 

